1. Field of the Invention
The present invention relates to an optical communication apparatus, and more specifically to an integral transmitter-receiver optical communication apparatus which is commonly used for both transmitting and receiving signals in the form of a laser beam modulated in accordance with an information signal.
2. Description of the Related Art
FIG. 5 shows an integral transmitter-receiver optical communication apparatus as an example to which the present invention is applicable. This optical communication apparatus includes a telescopic optical system 10, a light beam deflecting device 20 and a transmitter-receiver unit 30. The telescopic optical system 10 is used for both projecting and receiving a laser beam modulated by the information signal. In this illustrated example, the telescopic optical system 10 is constructed as a reflecting telescope. The light beam deflecting device 20 is positioned between the telescopic optical system 10 and the transmitter-receiver unit 30 to adjust the direction of the receiving light which enters the transmitter-receiver unit 30 through the telescopic optical system 10 and also the direction of the transmitting light which is emitted from the transmitter-receiver unit 30 to the telescopic optical system 10.
The transmitter-receiver unit 30 is provided with a semiconductor laser source 32 which emits a laser beam modulated by the modulator 31 in accordance with a transmission information signal. The semiconductor laser source 32 is constructed to emit the modulated laser beam so that S-polarized light thereof is reflected. The transmitter-receiver unit 30 is further provided with a polarization beam splitter (PBS) 33 on which the linearly polarized light emitted from the semiconductor laser source 32 is incident. The polarization beam splitter 33 reflects S-polarized light while allowing P-polarized light to pass therethrough. The S-polarized light that is reflected by the polarization beam splitter 33 is incident on the light beam deflecting device 20 via a xcex/4 retardation plate 34. The transmitter-receiver unit 30 is further provided, on a transmission light path of the polarization beam splitter 33, with a beam splitter 35 in order to receive the light signal transmitted from a complementing optical transmitter, which is positioned opposite to the optical communication apparatus. A light receiving element 36 and a position detecting sensor 37, each of which receives a modulated laser beam, are respectively positioned on two separate light paths split by the beam splitter 35. Accordingly, the light emitted by the aforementioned complementing optical transmitter to be received by the telescopic optical system 10 is turned into P-polarized light through the xcex/4 retardation plate 34. Subsequently, the P-polarized light passes through the polarization beam splitter 33 and then enters the beam splitter 35 to be split into two separate light beams so that the two separate light beams are incident on the light receiving element 36 and the position detecting sensor 37, respectively. A signal processing circuit 38 is connected to the light receiving element 36 to read out the information conveyed by the light received by the light receiving element 36.
The integral transmitter-receiver optical communication apparatus having the aforementioned structure is generally positioned opposite to the semiconductor laser beam of a complementing optical communication apparatus having an identical structure, wherein the transmission range of the laser beam emitted by the semiconductor laser beam 32 overlaps the transmission range of the semiconductor laser beam emitted by the complementing optical communication apparatus, so that the laser beam modulated by the modulator 31 can be received by the light receiving element 36 in each of the mutually complementing optical communication apparatuses.
In each of the mutually complementing optical communication apparatuses, the light beam deflecting device 20 maintains the parallelism of the transmitting laser beam which is incident thereon to be deflected outwards through the telescopic optical system 10, and also the parallelism of the received laser beam (which is emitted by the complementing optical communication apparatus) to be incident on the light beam deflecting device 20. The light beam deflecting device 20 can include a rotatable deflection mirror which can be driven about two axes (X and Y axes) which are orthogonal to each other. A rotational portion of the rotatable deflection mirror is coupled to an electromagnetic driver which includes coils and permanent magnets. This electromagnetic driver is driven in accordance with signals output from the position detecting sensor 37. The position detecting sensor 37 detects the variation in the position of the receiving light which enters the transmitter-receiver unit 30 to output a drive command signal to the electromagnetic driver through a controller 21 and an X/Y driver 22 to rotate the deflection mirror 20 about the X-axis and the Y-axis thereof, so that the receiving light enters the transmitter-receiver unit 30 at an appropriate position. The position of the deflection mirror 20 continues to be detected by the position detecting sensor 37 in a feed-back operation so that the parallelism of both the light transmitted by the transmitter and the light received by the receiver are maintained.
In the conceptual structure of the integral transmitter-receiver optical communication apparatus shown in FIG. 5, crosstalk does not occur, in theory, between the transmitting laser beam emitted from the semiconductor laser source 32 and the received laser beam incident upon the light receiving element 36 and the position detecting sensor 37. However, in practice, there is a possibility of such crosstalk occurring due to the polarization beam splitter 33 not being able to perfectly polarize the incident light (in fact, it is practically impossible to provide a polarization beam splitter having a polarization beam splitting thin layer therein through which the incident light is perfectly polarized, and hence, the occurrence of a small percentage of infiltrating (stray) light cannot be prevented), and/or due to the polarization beam splitter 33 and the beam splitter 35 being positioned very closely to each other.
The primary object of the present invention is to provide an integral transmitter-receiver optical communication apparatus, wherein the occurrence of a crosstalk between the transmitting light and the receiving light can be prevented. A more specific object of the present invention is to provide an integral transmitter-receiver optical communication apparatus wherein the transmitting light can be prevented from entering the side of the receiver, in the case where a polarization beam splitter and a beam splitter (i.e., a polarization beam splitting plane and a beam splitting plane) are positioned adjacent to each other.
To achieve the above-mentioned objects, according to the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device which includes: a transmitter having a laser source for emitting a laser beam modulated in accordance with a transmission information signal, a receiver having a position detecting sensor and a light receiving element which receive a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam which are incident thereon as two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter; and a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor. The beam splitting device includes: in order from the light beam deflecting device side, a polarization beam splitting plane which allows a first linearly polarized laser beam of the modulated laser beam emitted from the laser source to pass therethrough to proceed towards the light beam deflecting device, and reflects a second linearly polarized laser beam of the complementing modulated laser beam transmitted from the complementing transmitter, the second linearly polarized laser beam having a phase different from a phase of the first linearly polarized laser beam by 90 degrees; and a beam splitting plane for splitting the second linearly polarized laser beam reflected by the polarization beam splitting plane into two separate laser beams to be respectively received by the position detecting sensor and the light receiving element. The modulated laser beam emitted from the laser source has a non-circular shape of intensity distribution, a first length in a xcex8-parallel direction of a cross section taken along a plane perpendicular to the modulated laser beam being shorter than a second length in a xcex8-perpendicular direction of the cross section, the first length and the second length extending perpendicularly to each other; and wherein the orientation of the laser source is determined so that the xcex8-parallel direction becomes substantially parallel to an optical axis extending from the polarization beam splitting plane to the beam splitting plane.
Preferably, the polarization beam splitting plane and the beam splitting plane are respectively formed on first and second planes of a common prism which are orthogonal to each other.
Preferably, an afocal optical system positioned between the light beam deflecting device and the transmitter-receiver device is also provided.
Preferably, the transmitter-receiver device includes a xcex/4 retardation plate positioned between the afocal optical system and the polarization beam splitting plane.
Preferably, the light beam deflecting device includes an adjustable deflection mirror that is driven in accordance with the signal output from the position detecting sensor.
Preferably, the transmitter-receiver device includes a band-pass filter between the beam splitting plane and the light receiving element.
Preferably, the transmitter-receiver device includes a band-pass filter between the beam splitting plane and the position detecting sensor.
Preferably, the polarization beam splitting plane and the beam splitting plane are formed on the prism apart from each other by a predetermined distance.
Preferably, a casing is further provided in which the prism having the polarization beam splitting plane and the beam splitting plane is supported, the casing being provided with a light interceptive wall positioned around a boarder between the polarization beam splitting plane and the beam splitting plane.
Preferably, a casing in which the prism having the polarization beam splitting plane and the beam splitting plane is supported, the casing being provided, on a light path of the polarization beam splitting plane, with an opening for allowing light which is emitted from the semiconductor laser source to be reflected by the polarization beam splitting plane to exit the casing.
According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a laser source for emitting a laser beam modulated by transmission information signal; a telescopic optical system for transmitting the modulated laser beam and for receiving a complementing modulated laser beam transmitted from a complementing transmitter; a position detecting sensor; a light receiving element; a polarization beam splitting plane positioned between the laser source and the telescopic optical system; an adjustable deflection mirror positioned between the telescopic optical system and the polarization beam splitting plane and driven in accordance with a signal output from the position detecting sensor; and a beam splitting plane positioned adjacent to the polarization beam splitting plane for splitting a laser beam reflected by the polarization beam splitting plane into two separate laser beams to be respectively received by the light receiving element and the position detecting sensor. The polarization beam splitting plane allows a first linearly polarized laser beam of the modulated laser beam emitted from the laser source to pass therethrough to proceed towards the deflecting mirror, and reflects a second linearly polarized laser beam of the complementing modulated laser beam transmitted from the complementing transmitter, the second linearly polarized laser beam having a phase different from a phase of the first linearly polarized laser beam by 90 degrees. The beam splitting plane splits the second linearly polarized laser beam reflected by the polarization beam splitting plane into two separate laser beams to be respectively received by the light receiving element and the position detecting sensor. The modulated laser beam emitted from the laser source has a non-circular shape of intensity distribution, a first length in the xcex8-parallel direction of a cross section taken along a plane perpendicular to the modulated laser beam being shorter than a second length in the xcex8-perpendicular direction of the cross section, the first length and the second length extending perpendicularly to each other. The orientation of the laser source is determined so that the xcex8-parallel direction becomes substantially parallel to an optical axis extending from the polarization beam splitting plane to the beam splitting plane.
The present disclosure relates to subject matter contained in Japanese Patent Application Nos. 10-204551 (filed on Jul. 21, 1998) and 11-81376 (filed on Mar. 25, 1999) which are expressly incorporated herein by reference in their entireties.